Objecitves: NIOSH has prepared a criteria packet for occupational exposure to hot environments which includes a temperature-time limit for sedentary jobs. The literature in this area is very contradictory and additional research is necessary to clarify these reported discrepancies. The objective of this proposed study is to provide additional well controlled and precise data to support of refute the NIOSH criteria for "unimpaired mental performance" in hot environments. Method: A series of experiments in the environmental chamber will be conducted using these variables: five sedentary tasks (multiplication, motor coordination, reaction time, tracking and monitoring tasks); seven levels of temperature (between 80 degrees F-110 degrees F WBGT); and work periods between 15 and 120 minutes. Task performance scores will be statistically analyzed for all temperature time combinations. Subjects oral (T oral) and rectal (T rectal) temperatures will be evaluated as a function of environmental temperature and time on task.